Wireless communications system including a wireless device locator and related methods

ABSTRACT

A wireless communications system may include a plurality of wireless communications devices and a wireless device locator. More particularly, the wireless device locator may include at least one antenna and a transceiver connected thereto, and a controller for cooperating with the transceiver for transmitting a plurality of location finding signals to a target wireless communications device from among the plurality thereof. The target device may transmit a respective reply signal for each of the location finding signals. Additionally, the controller may also cooperate with the transceiver for receiving the reply signals, and it may determine a propagation delay associated with the transmission of each location finding signal and the respective reply signal therefor based upon a known device latency of the target device. As such, the controller may estimate a range to the target device based upon a plurality of determined propagation delays.

FIELD OF THE INVENTION

The present invention relates to the field of wireless communicationssystems, and, more particularly, to wireless location devices andrelated methods.

BACKGROUND OF THE INVENTION

Wireless location techniques are used in numerous applications. Perhapsthe most basic of these applications is for locating lost articles. Byway of example, published U.S. patent application No. 2003/0034887 toCrabtree et al. discloses a portable article locator system for locatinglost articles such as glasses, keys, pets, television remotes, etc. Moreparticularly, a wireless transceiver is attached to a person, animal, orother object. A handheld locator transmits a locator signal to thewireless transceiver which includes a unique address code of thetransceiver. If the received code matches that stored by the wirelesstransceiver, it sends a return signal back to the locator device. Thelocator device uses the return signal to determine the distance and/ordirection to the wireless transceiver from the user's location.

The locator device includes an antenna array which includes a pluralityof omni-directional antennas. The locator unit determines the bearing tothe wireless transceiver by switching between antennas in the antennaarray and using Doppler processing to determine a direction of awireless signal received from the transceiver. The distance to thewireless transmitter is also determined based upon the reception of thewireless signal at each of the antennas of the antenna array.Furthermore, in one embodiment, which is intended to avoid interferencebetween two or more locators in a common area, a plurality of locatorsignals may be sent from a locator at a standard repetition rate. Thelocator's receiver then only listens for responses during predeterminedwindows following each transmission.

In contrast, in some applications it is desirable to determine thelocation of an unknown signal transmitter. U.S. Pat. No. 5,706,010 toFranke discloses such a system in which a transmitter locator receives asignal from the unknown signal transmitter and processes the signal todetermine a bearing to the unknown signal transmitter. The transmitterlocator then sends an interrogating signal to the unknown signaltransmitter. Upon receiving the interrogating signal, the unknown signaltransmitter heterodynes the interrogation signal with its own carriersignal to generate an intermodulation return signal. A processor of thetransmitter locator measures the round-trip transit time from thetransmission of the interrogation signal to the reception of theintermodulation return signal. A range to the unknown signal transmitteris then calculated based upon the round-trip transit time.

Still another application in which locating a wireless communicationsdevice is often necessary is in cellular telephone networks. That is, itmay be necessary to locate particular cellular telephone users for lawenforcement or emergency purposes, for example. U.S. Pat. No. 6,292,665to Hildebrand et al., which is assigned to the present assignee,discloses a method for geolocating a cellular phone initiating a 911call. A base station transceiver transmits a supervisory audio tone(SAT), which is automatically looped back by the calling cellular phone.Returned SAT signals are correlated with those transmitted to determinethe range of the cellular phone. In addition, incoming signals from thecellular phone, such as the returned SAT signals, are received by aphased array antenna and subjected to angle of arrival processing todetermine the direction of the cellular phone relative to the basestation. The cellular phone is geolocated based upon the angle ofarrival and the range information. A correction factor provided by themanufacturer of a given cellular telephone is used to account for theloopback path delay through the phone.

One additional area in which wireless device location can be importantis in wireless networks, such as wireless local area networks (WLANs) orwide area networks (WANs), for example. A typical prior art approach tolocating terminals within a WLAN includes locating a plurality ofreceivers at fixed locations within a building, for example, and thendetermining (i.e., triangulating) the position of a terminal based upona signal received therefrom at each of the receivers.

Another prior art approach for wireless terminal location is to use adirection finding (DF) device which includes a directional antenna forreceiving signals when pointed in the direction of a transmitting node.An example of a portable DF device for WLANs is the Yellowjacket 802.11awi-fi analysis system from Berkeley Varitronics. This device uses apassive DF technique, i.e., it does not solicit any signals from aterminal but instead waits for the terminal to transmit signals beforeit can determine the direction of the transmission.

Despite the advantages of such prior art wireless communications devicelocators, additional wireless location features may be desirable invarious applications.

SUMMARY OF THE INVENTION

In view of the foregoing background, it is therefore an object of thepresent invention to provide a wireless communications device locatorwhich provides enhanced location features and related methods.

This and other objects, features, and advantages in accordance with thepresent invention are provided by a wireless communications system whichmay include a plurality of wireless communications devices each having adevice type associated therewith from among a plurality of differentdevice types. Further, each device type may have a known device latencyassociated therewith. The system may also include a wireless devicelocator. More particularly, the wireless device locator may include atleast one antenna and a transceiver connected thereto, and a controllerfor cooperating with the transceiver for transmitting a plurality oflocation finding signals to a target wireless communications device fromamong the plurality of wireless communications devices. The targetwireless communications device may transmit a respective reply signalfor each of the location finding signals.

Additionally, the controller of the wireless device locator may alsocooperate with the transceiver for receiving the reply signals, and itmay determine a propagation delay associated with the transmission ofeach location finding signal and the respective reply signal therefor.This may be done based upon the known device latency of the targetwireless communications device. As such, the controller may estimate arange to the target wireless communications device based upon aplurality of determined propagation delays.

In other words, the wireless device locator advantageously providesactive range finding. In other words, the wireless device locatorprompts the target wireless communications device to send reply signalsusing the location finding signals, rather than passively waiting untilthe target wireless communications device begins transmitting. Thisallows for quicker and more efficient device location.

Furthermore, by estimating the range based upon a plurality ofpropagation delays, the wireless device locator mitigates the effects ofvariations in the device latency time. That is, while the targetwireless communication device has a known device latency, there willnecessarily be some amount of variance from one transmission to thenext. Using a plurality of propagation delays associated with differenttransmissions provides a significantly more accurate approximation ofthe device latency time and, thus, a more accurate range estimation. Byway of example, the controller may estimate the range based upon anaverage (e.g., mean, median, mode, etc.) of the propagation delays.

In addition, each wireless communications device may have a uniqueidentifier (UID) associated therewith, and the controller may insert theUID for the target wireless communications device in each of thelocation finding signals. Furthermore, the target wirelesscommunications device may generate respective reply signals based uponthe UID in the location finding signals. That is, the target wirelesscommunications device will act upon the location finding signals becausethese signals include its UID, whereas the other wireless communicationsdevice will not.

The target wireless communications device may generate unsolicitedsignals including the UID thereof. As such, the controller may cooperatewith the transceiver to receive at least one unsolicited signal from thetarget device, and the controller may also determine the UID for thetarget device from the at least one unsolicited signal. Thus, if the UIDof a target wireless communications device is not already known, thewireless device locator may passively “listen” for unsolicited signalstherefrom (i.e., signals that the wireless communications device did notsolicit) and determine the UID based thereon.

Additionally, the controller may also determine the device type of thetarget wireless communications device based upon the UID. By way ofexample, the UIDs may include media access control (MAC) addresses ofrespective wireless communications devices. Accordingly, the controllermay determine the device type of the target wireless communicationsdevice based upon the MAC address in some applications.

In accordance with another advantageous aspect of the invention, the atleast one antenna may be a plurality of antennas, and the controller maycooperate with the plurality of antennas to determine a bearing to thetarget wireless communications device based upon at least one of thereceived reply signals. More particularly, the bearing may be athree-dimensional bearing, which may be particularly useful for locatingwireless communications devices within a multi-story building, forexample. In particular, the antenna(s) may be one or more directionalantennas, for example. Further, the wireless device locator may furtherinclude a portable housing carrying the at least one antenna, thetransceiver, and the controller.

The wireless device locator may be used with numerous type of wirelesscommunications device. For example, the wireless communications devicesmay be wireless local area network (WLAN) devices, mobile ad-hoc network(MANET) devices, and cellular communications devices.

A method aspect of the invention is for locating a target wirelesscommunications device from among a plurality of wireless communicationsdevices, such as those discussed briefly above. The method may includetransmitting a plurality of location finding signals to the targetwireless communications device, and receiving a respective reply signalfor each of the location finding signals therefrom. The method mayfurther include determining a propagation delay associated with thetransmission of each location finding signal and the respective replysignal therefor based upon the known device latency of the targetwireless communications device. As such, a range to the target wirelesscommunications device may be estimated based upon a plurality ofdetermined propagation delays.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic block diagram of a wireless communications system inaccordance with the present invention including a wireless local areanetwork (WLAN) and wireless device locator for locating WLAN devicesthereof.

FIG. 2 is a schematic block diagram generally illustrating thecomponents of the wireless device locator of FIG. 1.

FIG. 3 is a graph illustrating the signal propagation delay and devicelatency components used by the controller of FIG. 2 to estimate range.

FIG. 4 is a schematic block diagram illustrating an embodiment of thewireless device locator of FIG. 2 for a WLAN implementation.

FIG. 5 is a schematic block diagram illustrating in greater detail anembodiment of the transceiver of the wireless device locator of FIG. 4.

FIGS. 6 and 7 are histograms illustrating range estimation test resultsperformed using the wireless device locator of FIG. 4.

FIG. 8 is a graph illustrating bearing determination in accordance withthe present invention.

FIGS. 9 and 10 are schematic block diagrams illustrating alternateembodiments of the wireless communications system of FIG. 1 including amobile ad-hoc network (MANET) and a cellular network, respectively.

FIG. 11 is a flow diagram illustrating a wireless device location methodin accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout, and prime and multiple primenotation are used to indicate similar elements in different embodiments.

Referring initially to FIGS. 1 and 2, a wireless communications system30 illustratively includes a wireless local area network (WLAN) 31 and awireless location device 32. The WLAN 31 illustratively includes anaccess point 33 (e.g., a server) and a plurality of WLAN devices orterminals which communicate therewith wirelessly, such as the laptopcomputers 34, 35, and the desktop computer 36. Various WLAN protocolsmay be used in accordance with the present invention for such wirelesscommunications (e.g., IEEE 802.11, Bluetooth, etc.), as will beappreciated by those of skill in the art. Moreover, it will also beappreciated that additional access points and/or other numbers ofwireless communications devices may be used, even though only a fewnumber thereof are shown for clarity of illustration. Further, numerousother types of WLAN enabled wireless communications devices (e.g.,personal data assistants, etc.) may also be used, as will be furtherappreciated by those skilled in the art.

Each wireless communications device 34–36 in the WLAN 31 has a devicetype associated therewith from among a plurality of different devicetypes. More particularly, the device type may signify the particularmanufacturer and/or model of a given WLAN card or chip set used therein.In some embodiments, it may also signify the standard the devicecomplies with (e.g., IEEE 802.11).

The device type is important in that different device types will haveknown device latencies associated therewith. For example, different WLANcards or chip sets will have a certain latency associated with the timethey take to process a received signal and generate an acknowledgementreply thereto. These delay times may be fairly consistent acrossdifferent models from a same manufacturer, or they may varysignificantly. Additionally, WLAN protocols such as IEEE 802.11 have aspecified interframe spacing associated therewith, as will beappreciated by those skilled in the art. Thus, in circumstances wherethe interframe spacing requirements are closely adhered to, the latencyof a given WLAN card or chip set will be substantially equal to theinterframe spacing.

The wireless device locator 32 illustratively includes an antenna 39 anda transceiver 41 connected thereto, as well as a controller 42 connectedto the transceiver. These components may conveniently be carried by aportable housing 43 in some embodiments, although they could beimplemented in a more stationary embodiment, if desired. In theillustrated example, the antenna 39 is a directional antenna, althoughomni-directional antennas may also be used, as will be appreciated bythose skilled in the art. It will also be appreciated that variousantenna/transceiver combinations may be used. As will be discussedfurther below, more than one antenna may be used in certain embodimentsto provide bearing determination capabilities, and separate transceiversmay optionally be used for respective antennas, if desired.

Operation of the wireless device locator 32 will now be described withreference to FIG. 3. The controller 42 cooperates with the transceiver41 for transmitting a plurality of location finding signals to a targetwireless communications device to be located from among the plurality ofwireless communications devices. In the present example, the laptop 34is the target device.

As will be appreciated by those skilled in the art, each WLAN device34–36 in the network 31 will have a unique identifier (UID) associatedtherewith which is used in signals transmitted between the respectivedevices and the access point 33. The UID distinguishes the devices 34–36from one another so that each device only acts upon or responds tosignals intended for it, and so the access point 33 knows which deviceit is receiving signals from.

Depending upon a given implementation, the wireless locator device 32may or may not know the UID of the target device 34 before hand. Forexample, in some embodiments the wireless device locator 32 coulddownload the UID from the access point 33 (either wirelessly or over awired network connection, for example). This may be the case when tryingto locate a node in a LAN where the node is already registered with thenetwork. However, if the UID is not known, the wireless device locator32 may passively listen to the target device 34 for unsolicited signalsbeing transmitted therefrom. This feature may be advantageous for lawenforcement applications, or for locating an interfering node that isnot registered with a particular network but causes interferencetherewith, for example. By “unsolicited” signals it is meant that thesesignals are not solicited by the wireless device locator 32 itself,although such signals may have been solicited from another source (e.g.,the access point 33).

The controller 42 cooperates with the transceiver 41 to receive one ormore of the unsolicited signals, and the controller determines the UIDfor the target device 34 therefrom. Of course, the method by which thecontroller 42 determines the UID from the unsolicited signal will dependupon the given implementation, and whether or to what degree suchsignals are encrypted.

Additionally, the controller 42 may also determine the device type ofthe target wireless communications device 34 based upon the UID thereof.By way of example, the UIDs may include media access control (MAC)addresses of respective wireless communications devices. The MACaddresses may be specific to a particular type of device manufacturer,or indicate a particular operational protocol with which the device isoperating, as will be appreciated by those skilled in the art.Accordingly, the controller may determine the device type of the targetwireless communications device 34 based upon the MAC address thereof insome applications.

As such, to locate the target device 34, the controller inserts the UIDtherefor in each of the location finding signals. By way of example, thelocation finding signal may include the UID of the target device 34 in aheader packet and a valid but empty data packet. This will force thetarget device 34 to generate a reply signal acknowledging receipt of thelocation finding signal (i.e., an ACK signal). Of course, various otherlocation finding signals could be used to cause the target terminal 34to generate an ACK signal, as will be appreciated by those skilled inthe art. The controller 42 cooperates with the transceiver 41 forreceiving the reply signals from the target device 34 via the antenna39. The location finding signals and reply signals may be radiofrequency (RF), microwave, optical, or other suitable types of signals,as will be appreciated by those skilled in the art.

The controller 42 determines the propagation delay associated with thetransmission of each location finding signal and the respective replysignal therefor, and it uses this propagation delay to estimate a rangeto the target device 34. However, the propagation delay has to first bedetermined based upon the total round trip time from the sending of thelocation finding signal to the reception of the respective reply signal.

The total round trip time will include several components. Referringmore particularly to FIG. 3, the first component is the time associatedwith transmitting a location finding signal 45, which is illustratedwith an arrow. That is, this is the time from the beginning of thelocation finding signal transmission (time t₀) to end thereof (time t₁).Two time axes are shown in FIG. 3. The top or upper axis representsevents that occur at the target device 34, while the bottom or loweraxis represents events that occur at the wireless device locator 32.

The second component of the round trip time is the propagation delay ortime t_(PD1) it takes for the location finding signal 45 to travel fromthe wireless device locator 32 to the target device 34 (i.e., from timet₁ to t₂). The third component of the round trip time is the devicelatency t_(DL) of the target device 34 (i.e., form time t₂ to t₃). Thisis the time it takes the target device 34 to receive, process, andtransmit a reply signal 46 responsive to the location finding signal 45.The final components of the round trip time are propagation delayt_(PD2) of the reply signal 46 (i.e., from time t₃ to t₄), and thereception time thereof by the wireless device locator 32 (i.e., fromtime t₄ to t₅).

The controller 42 will know the times associated with the transmissionof the location finding signal 45 (i.e., from time to t₀ to t₁), as wellas the time associated with the reception of the reply signal 46 (i.e.,from time t₄ to t₅) for each round trip, since these can be readilymeasured by the controller. The quantities that the controller 42 willnot know are the propagation delays t_(PD1), t_(PD2) and the actualdevice latency t_(DL).

Yet, as noted above, the controller 42 will have access to the knowndevice latency (i.e., a mean latency) for the given device type of thetarget device 34, which provides a close approximation of the actualdevice latency t_(DL). The known device latency could be a measuredvalue based upon collected data, it could be provided by manufacturers,or it could be based upon a value set in a communications standard, asdiscussed above, for example.

As will be appreciated by those skilled in the art, the actual devicelatency will likely vary somewhat from one transmission to the next forany wireless communications device, potentially by as little as a fewnanoseconds to a few microseconds, depending upon device configurations,processing loads, etc. Accordingly, a close approximation of the totalpropagation delay (i.e., time t_(PD1)+time t_(PD2)) may therefore beobtained by substituting the known device latency for the actual devicelatency t_(DL), and subtracting this value from the time between timest₁ and t₄. Dividing the total propagation delay by two (since bothpropagation delays may be considered equal or substantially equal for astationary or relatively slow moving target device 34) and multiplyingthis by the speed of light gives the estimated distance to the targetdevice 39, based upon the single propagation delay associated with thesignal pair 45, 46.

Yet, as noted above, device latencies tend to vary from one transmissionto the next. Since the location finding signals and reply signals aretraveling at the speed of light, such variances can make a significantdifference in the estimated distances. More particularly, light travelsapproximately 1000 ft. in one microsecond. Thus, if the device latencyvaries by one microsecond from one transmission to the next, theestimated distance to the target device 34 would similarly vary by 1000ft. or so, which likely will be an unacceptable accuracy for manyapplications.

In accordance with the present invention, the controller 42advantageously estimates the range to the target device 34 not solelybased upon a single measured propagation delay, but rather upon aplurality thereof. More particularly, by estimating the range based upona plurality of propagation delays, the wireless device locator 32mitigates the effects of the variations in the actual device latencytime. This provides a significantly more accurate approximation of thedevice latency time and, thus, a more accurate range estimation. By wayof example, the controller 42 may estimate the range based upon anaverage of the propagation delays, though other suitable statisticalfunctions may also be used (e.g., mean, median, mode, etc.). Of course,it should be noted that the average may be taken on the entire roundtrip delay instead of first subtracting out the known device latency asdescribed above. That is, the same result may be obtained by firsttaking the average and then subtracting out the known device latency, aswill be appreciated by those skilled in the art.

An exemplary embodiment of the present invention is now described withreference to FIGS. 4 and 5. The wireless device locator 32′ may use apersonal data assistant (PDA) as the controller 42′, although a personalcomputer (PC) or other suitable computing device may also be used. Moreparticularly, the PDA 42′ illustratively includes a graphical userinterface (GUI) 50′, and a received signal strength indication (RSSI)processing module 51′ for cooperating with the transceiver 41′ toperform above-described range estimation processing operations. Moreparticularly, the RSSI module 51′ may be implemented as a softwaremodule which is run on the PDA 42′, as will be appreciated by thoseskilled in the art, and which cooperates with the GUI to provide rangeestimates to a user.

The PDA 50′ also illustratively includes a battery 52′, which mayconveniently be used for powering the various transceiver 41′components, as shown. Of course, it will be appreciated that separatebatteries may be used, or one or more components of the wireless devicelocator 32′ may be powered by an external (e.g., AC) source. Thetransceiver 41′ operates in accordance with the IEEE 802.11b standardand includes a MAC-less 802.11b radio 58′ and a field-programmable gatearray (FPGA) 53′ connected thereto. The FPGA 53′ illustratively includesa packet building module 54′, a radio configuration module 55′, areceiver filtering module 56′, and a simple MAC processing module 57′for processing the location finding signals and reply signals andcommunicating with the radio 53′ in accordance with the 802.11bstandard, as will be appreciated by those skilled in the art.

More specifically, the MAC-less radio 58′ may be a GINA model RF modulefrom GRE America, Inc., and the FPGA 53′ may be a module EPXA10 fromAltera Corp. The hardware components of the FPGA 53″ illustrativelyinclude an ARM922T processor 60″, block RAM 61″ therefor, aserial/universal serial bus (USB) interface 62″, and a programmablelogic section 63″. Additional circuitry including an oscillator 64″,power management circuitry (i.e., regulators, microprocessor supervisor,etc.) 65″, and a programmable read-only memory (PROM)/boot flash memory66″ are connected thereto as shown, as will be appreciated by thoseskilled in the art.

Referring now to FIGS. 6–7, a test was conducted in accordance with thepresent invention in which approximately 1500 location finding signalswere transmitted to a stationary wireless IEEE 802.11 device. The timeit took to receive the reply signal was measured by ticks of an internalclock of the controller 42, where each tick represents 7.567 ns. FromFIG. 6 it may be seen that the reply signals from the target device werereturned within between about 20,960 and 21,045 clock ticks, where thetransmission of the respective location signals each began at 0 clockticks. Moreover, if this range is divided into equal sections or bins,the frequency (i.e., number) of round trip times that fell within eachof the bins is shown in FIG. 7.

Plotting various statistical functions of the measured clock ticksamples (such as the mean and the mode) versus the known distance to thetarget device allowed statistical curve-fitting to take place, as shownin FIG. 6. It was determined from the test results that taking the meanof the samples provided the most accurate range estimation. Moreparticularly, the ranges to several 802.11b target devices at varyingdistances were estimated using this approach, and the worst case errorfor the estimated range was never more than 20 ft. Preferably, thelocation finding signals are transmitted over a relatively shortinterval (a few seconds or less) so that if the target device is movingthe accuracy of the results will not be significantly diminished. Ofcourse, various numbers of location finding signals and transmissionintervals may be used depending upon the particular implementation, aswill be appreciated by those skilled in the art.

In accordance with another advantageous aspect of the invention,multiple antennas 39 a″, 39 b″ (FIG. 5) may be used to provide targetbearing in addition to the estimated range. Referring more particularlyto FIG. 8, bearing determination in the case where the antennas 39 a″,39 b″ are directional antennas will now be described. The antennas 39a″, 39 b″ have respective reception patterns 70 a, 70 b, which may beorthogonal to one another (i.e., the former is directed along thex-axis, while the latter is directed along the y-axis).

The target device is at a point P, which is within the receptionpatterns 70 a, 70 b. Each of the antenna gain patterns 70 a and 70 b canbe measured and known to the locator, and represented by gain functionsG1(θ) and G2(θ) where θ represents the angle of deviation from aparticular reference direction.

As such, to determine the line of bearing to the target device, thereceived signal strength is measured from each of the antennas 70 a, 70b, respectively. Based upon this information, the controller 42′ maythen find the angle θ_(t) using the relationshipG1(θ_(t))−G2(θ_(t))=P1−P2, where P1 and P2 is the received signal poweroff antenna 1 and antenna 2, respectively. In other words, thedifference in the signal strength received between the two antennas(P1−P2) should equal the difference in the antenna gain of the twoantennas at the angle of the line of bearing (G1(θ_(t))−G2(θ_(t))) Thus,the target line of bearing to the target device is at θ_(t). It shouldbe noted that it is possible that more than one angle θ may satisfy therelationship G1(θ_(t))−G2(θ_(t))=P1−P2. These multiple angles representa line of bearing ambiguity that can easily be resolved by makingmultiple measurements, as can be appreciated by those skilled in theart.

As noted above, more than one transceiver 41′ may be used in certainembodiments, which would allow signal strength measurements to be takenbased upon a same reply signal from the target device. However, if onlya single transceiver 41′ is used, the controller 42′ may alternate whichantenna 70 a, 70 b is receiving and measure the received signal strengthof successive signals, for example. Moreover, the bearing may bedetermined in three dimensions, if desired, which may be particularlyuseful for locating wireless communications devices within a multi-storybuilding, for example, as will be appreciated by those skilled in theart.

While the present invention has been described above with reference to aWLAN wireless device locator 32′, it will be appreciated by thoseskilled in the art that it may also be used in other wirelesscommunications systems with other types of wireless communicationsdevices. Referring more particularly to FIG. 9, a mobile ad-hoc network(MANET) system 90 illustratively includes a wireless device locator 92including an antenna 99, such as those described above, and a MANET 91.More particularly, the MANET includes MANET nodes or devices 93–96, ofwhich the node 94 is the target node in the illustrated example. Here,the wireless device locator 92 performs range and/or bearing estimationin the same manner described above, except that it will operate inaccordance with the appropriate MANET protocol used within the system90, as will be appreciated by those skilled in the art.

Another embodiment is illustrated in FIG. 10, in which a wireless devicelocator 102 having an antenna 109 is used within a cellularcommunications system 100 for locating cellular devices (e.g., cellulartelephones) 104–106 in cellular network 101. The cellular devices104–106 place and receive calls via a cellar tower 103, as will beappreciated by those skilled in the art. In the illustrated example, thetarget device is the cell phone 104. Here again, the wireless devicelocator 102 will communicate using the appropriate operating protocolbeing used in the cellular network 101 (e.g., code-division multipleaccess (CDMA), short message service (SMS), etc.), as will beappreciated by those skilled in the art.

Turning now additionally to FIG. 11, a method aspect of the invention isfor locating a target wireless communications 34 device from among aplurality of wireless communications devices 34–36. Beginning at Block110, if the UID for the target device 34 is unknown, the controller 42may determine the UID from unsolicited signals transmitted by the targetdevice, for example, as described above (Block 112). Of course, in someembodiments, the controller 42 may download the signals from a networkaccess point 33, etc., as also described above.

Once the UID for the target wireless communication device 34 is known,location finding signals are transmitted to the target wirelesscommunications device, at Block 113, and respective reply signals foreach of the location finding signals are received therefrom, at Block114. If the device type (and, thus, the known device latency) are known,at Block 115, then the propagation delay associated with thetransmission of each location finding signal and the respective replysignal therefor is determined based upon the known device latency of thetarget wireless communications device 34, at Block 116. As such, a rangeto the target wireless communications device 34 is estimated based upona plurality of determined propagation delays (Block 117), as previouslydiscussed above, thus concluding the illustrated method (Block 118).

Of course, if the device type is unknown, the controller 42 maydetermine the device type from the reply signal (Block 119), asdiscussed above, or by other suitable methods which will be appreciatedby those skilled in the art. It should be noted that while this step isshown as occurring after the receipt of the reply signals in theillustrated example, the device type determination may be performedprior thereto, such as while determining the UID, for example.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

1. A wireless communications system comprising: a plurality of wirelesscommunications devices each having a device type associated therewithfrom among a plurality of different device types, each WLAN devicehaving a unique identifier (UID) associated therewith, and each devicetype having a known device latency associated therewith; and a wirelessdevice locator comprising at least one antenna and a transceiverconnected thereto, and a controller for cooperating with saidtransceiver for transmitting a plurality of location finding signals toa target wireless communications device from among said plurality ofwireless communications devices and inserting the UID for said targetwireless communications device in each of the location finding signals;said target wireless communications device transmitting a respectivereply signal for each of said location finding signals based upon theUID in the location finding signals; said controller of said wirelessdevice locator also for cooperating with said transceiver for receivingthe reply signals, determining a propagation delay associated with thetransmission of each location finding signal and the respective replysignal therefor based upon the known device latency of said targetwireless communications device, and estimating a range to said targetwireless communications device based upon a plurality of determinedpropagation delays.
 2. The wireless communications system of claim 1wherein said controller estimates the range based upon an average of thepropagation delays.
 3. The wireless communications system of claim 1wherein said target wireless communications device generates unsolicitedsignals including the UID thereof; wherein said controller cooperateswith said transceiver to receive at least one unsolicited signal fromsaid target device; and wherein said controller determines the UID forsaid target wireless communications device from the at least oneunsolicited signal.
 4. The wireless communications system of claim 3wherein said controller determines the device type of said targetwireless communications device based upon the UID thereof.
 5. Thewireless communications system of claim 4 wherein the UIDs comprisemedia access control (MAC) addresses of respective wirelesscommunications devices, and wherein said controller determines thedevice type of said target wireless communications device based upon theMAC address thereof.
 6. The wireless communications system of claim 1wherein said at least one antenna comprises a plurality of antennas; andwherein said controller cooperates with said plurality of antennas todetermine a bearing to said target wireless communications device basedupon at least one of the received reply signals.
 7. The wirelesscommunications system of claim 6 wherein the bearing is athree-dimensional bearing.
 8. The wireless communications system ofclaim 1 wherein said at least one antenna comprises at least onedirectional antenna.
 9. The wireless communications system of claim 1wherein said wireless device locator further comprises a portablehousing carrying said at least one antenna, said transceiver, and saidcontroller.
 10. The wireless communications system of claim 1 whereinsaid wireless communications devices comprise wireless local areanetwork (WLAN) devices.
 11. The wireless communications system of claim1 wherein said wireless communications devices comprise mobile ad-hocnetwork (MANET) devices.
 12. The wireless communications system of claim1 wherein said wireless communications devices comprise cellularcommunications devices.
 13. A wireless communications system comprising:a plurality of wireless local area network (WLAN) devices each having adevice type associated therewith from among a plurality of differentdevice types, each WLAN device having a unique identifier (UID)associated therewith, and each device type having a known device latencyassociated therewith; and a wireless device locator comprising at leastone antenna and a transceiver connected thereto, and a controller forcooperating with said transceiver for transmitting a plurality oflocation finding signals to a target WLAN device from among saidplurality of WLAN devices and inserting the UID for said target wirelesscommunications device in each of the location finding signals; saidtarget WLAN device transmitting a respective reply signal for each ofsaid location finding signals based upon the UID in the location findingsignals; said controller of said wireless device locator also forcooperating with said transceiver for receiving the reply signals,determining a propagation delay associated with the transmission of eachlocation finding signal and the respective reply signal therefor basedupon the known device latency of said target WLAN device, and estimatinga range to said target WLAN device based upon an average of a pluralityof determined propagation delays.
 14. The wireless communications systemof claim 13 wherein said target WLAN device generates unsolicitedsignals including the UID thereof; wherein said controller cooperateswith said transceiver to receive at least one unsolicited signal fromsaid target WLAN device; and wherein said controller determines the UIDfor said target WLAN device from the at least one unsolicited signal.15. The wireless communications system of claim 14 wherein saidcontroller determines the device type of said target WLAN device basedupon the UID thereof.
 16. The wireless communications system of claim 15wherein the UIDs comprise media access control (MAC) addresses ofrespective WLAN devices, and wherein said controller determines thedevice type of said target WLAN device based upon the MAC addressthereof.
 17. The wireless communications system of claim 13 wherein saidat least one antenna comprises a plurality of antennas; and wherein saidcontroller cooperates with said plurality of antennas to determine abearing to said target WLAN device based upon at least one of thereceived reply signals.
 18. A wireless device locator for locating atarget wireless communications device having a unique identifier (UID)associated therewith, the wireless device locator comprising: at leastone antenna and a transceiver connected thereto; and a controller forcooperating with said transceiver for transmitting a plurality oflocation finding signals to the target wireless communications device,inserting the UID for the target wireless communications device in eachof the location finding signals, and receiving a respective reply signalfor each of said location finding signals generated by the targetwireless communications device based upon the UID in the locationfinding signals, determining a propagation delay associated with thetransmission of each location finding signal and the respective replysignal therefor based upon a known device latency of the target wirelesscommunications device, and estimating a range to the target wirelesscommunications device based upon a plurality of determined propagationdelays.
 19. The wireless device locator of claim 18 wherein saidcontroller estimates the range based upon an average of the propagationdelays.
 20. The wireless device locator of claim 18 wherein the targetwireless communications device generates unsolicited signals includingthe UID thereof; wherein said controller cooperates with saidtransceiver to receive at least one unsolicited signal from the targetdevice; and wherein said controller determines the UID for the targetwireless communications device from the at least one unsolicited signal.21. The wireless device locator of claim 18 wherein said at least oneantenna comprises a plurality of antennas; and wherein said controllercooperates with said plurality of antennas to determine a bearing to thetarget wireless communications device based upon at least one of thereceived reply signals.
 22. The wireless device locator of claim 18wherein said at least one antenna comprises at least one directionalantenna.
 23. The wireless device locator of claim 18 wherein saidwireless device locator further comprises a portable housing carryingsaid at least one antenna, said transceiver, and said controller. 24.The wireless device locator of claim 18 wherein the target wirelesscommunications device comprises a wireless local area network (WLAN)device.
 25. The wireless device locator of claim 18 wherein the targetwireless communications device comprises a mobile ad-hoc network (MANET)device.
 26. The wireless device locator of claim 18 wherein the targetwireless communications device comprises a cellular communicationsdevice.
 27. A method for locating a target wireless communicationsdevice from among a plurality of wireless communications devices, eachwireless communications device having a device type associated therewithfrom among a plurality of different device types, each WLAN devicehaving a unique identifier (UID) associated therewith, and each devicetype having a known device latency associated therewith, the methodcomprising: transmitting a plurality of location finding signals to thetarget wireless communications device, inserting the UID for the targetwireless communications device in each of the location finding signals,and receiving a respective reply signal for each of the location findingsignals generated by the target wireless communications device basedupon the UID in the locations signals; determining a propagation delayassociated with the transmission of each location finding signal and therespective reply signal therefor based upon the known device latency ofthe target wireless communications device; and estimating a range to thetarget wireless communications device based upon a plurality ofdetermined propagation delays.
 28. The method of claim 27 wherein thecontroller estimates the range based upon an average of the propagationdelays.
 29. The method of claim 27 wherein the target wirelesscommunications device generates unsolicited signals including the UIDthereof; and further comprising: receiving at least one unsolicitedsignal from the target device; and determining the UID for the targetwireless communications device from the at least one unsolicited signal.30. The method of claim 29 further comprising determining the devicetype of the target wireless communications device based upon the UIDthereof.
 31. The method of claim 27 further comprising determining abearing to the target wireless communications device based upon at leastone of the received reply signals.
 32. The method of claim 27 whereinthe target wireless communications device comprises a wireless localarea network (WLAN) device.
 33. The method of claim 27 wherein thetarget wireless communications device comprises a mobile ad-hoc network(MANET) device.
 34. The method of claim 27 wherein the target wirelesscommunications device comprises a cellular communications device.